Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
Various fixed pattern noise, such as vertical and horizontal fixed pattern noises, may cause unwanted noise in an image. Such fixed pattern noise may be caused by consistent differences in the individual responsivity of readout circuits, for example. Consistent variations between the readout of different rows of an array, for example, may produce the unwanted variations in the image.
Many techniques have been employed to mitigate the effects of fixed pattern noise and enhance image sensor performance. However, some of these methods may not entirely eliminate the effects of the vertical fixed pattern noise.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.